Evolution and Systematics
Molecular Biology and Genetics
Statistics of barcoding coverage
Specimens with Sequences:2405
Specimens with Barcodes:2313
Species With Barcodes:159
Leukoma is a genus of saltwater clams, marine bivalve mollusks in the family Veneridae, the Venus clams. This genus of bivalves has been exploited by humans since prehistory; for example, the Chumash peoples of California harvested this genus from Morro Bay in approximately 1000 AD.
Species within the genus Leukoma include:
- Veneridae, 2001
- C.M.Hogan, 2008
The Veneridae or venerids, common name the Venus clams, are a very large family of minute to large, saltwater clams, marine bivalve molluscs. There are over 500 living species of venerid bivalves, most of which are edible, and many of which are exploited as a food source.
Many of the most important edible species are commonly known (in the USA) simply as "clams". Venerids make up a significant proportion of the world fishery of edible bivalves. The family includes some species that are important commercially, such as (in the USA) the hard clam or quahog, Mercenaria mercenaria.
The classification within the family Veneridae has been controversial at least since the 1930s. The most used classification is that of Keen (1969) which recognises 12 subfamilies, listed below. Some common species have been moved between genera (including genera in different subfamilies) because of repeated attempts to bring a more valid organization to the classification or taxonomy of the family, therefore changes in the generic name of species are frequently encountered.
The characters used for classifying this group still tend to be superficial, focusing on external features, especially those of the shell. Venerid clams are characterized as bivalves with an external posterior ligament, usually a well demarcated anterior area known as the lunule, and three interlocking structures (called cardinal teeth) in the top of each valve; in several of the subfamilies there are also anterior lateral teeth, anterior to the cardinal teeth: one in the left valve, and two (sometimes obscure) in the right valve. The inner lower peripheries of the valves can be finely toothed or smooth.
Shell sculpture tends to be primarily concentric, but radial and divaricating ornamentation (see Gafrarium), and rarely spines (Pitar lupanaria for example) occur on some. One small subfamily, Samarangiinae, is created for a unique and rare clam found in coral reefs with an outer covering of cemented sand or mud that texturally camouflages it while enhancing the thickness of the shell. Several Venerid clams have overall shell shapes that are adapted to their environment. Tivela species, for example, have the triangular outline of the surf clams in other bivalve families, and occur often in surf zones. Some Dosinia species are almost disc-like in shape and reminiscent of Lucinid bivalves; both types of circular bivalves tend to burrow relatively deeply into the sediment. Further reclassification is to be expected as the results of current research in molecular systematics on the group appear in the literature.
Venerids have rounded or oval solid shells with the umbones (projections) inturned towards the anterior end. There are three or four cardinal teeth on each valve. The siphons are short and united, except at the tip, and are not very long. The foot is large.
Subfamilies according to Keen (1969)
List of genera in the family Veneridae
(may be incomplete)
- Barrett, J. H. and C. M. Yonge, 1958. Collins Pocket Guide to the Sea Shore. P. 158. Collins, London
- Keen, A. M. (1969). Superfamily Veneracea. pp. 670–690, in: Leslie Reginald Cox et al., Part N [Bivalvia], Mollusca 6, vols. 1 and 2: xxxvii + 952 pp. Part of Raymond C. Moore, ed., Treatise on Invertebrate Paleontology. Lawrence, Kansas (Geological Society of America & University of Kansas).
- Powell A. W. B., New Zealand Mollusca, William Collins Publishers Ltd, Auckland, New Zealand 1979 ISBN 0-00-216906-1
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